What is the difference between an AR-10/LR-308?

The family of rifles generally referred to as "AR-10"s or "AR-308"s encompasses a variety of rifles from a variety of manufacturers. Although similar in appearance and function, different rifles may have different upper receiver designs with parts that may or may not be interchangeable. This situation makes shopping for a free float quad rail or handguard a bit complicated.

AR-10 style rifles have a few different commonly used barrel nut designs (the attachment point for a free float handguard), each of which is compatible only with a free float quad rail or handguard built specifically for that design. The two most common standards are for the original AR-10 and for the DPMS LR-308. Both of these standards are now used by a number of different manufacturers.

Armalite AR-10 Style Handguards

The original AR-10 was developed in the 1950’s by ArmaLite, who still owns the AR-10 trademark and sells the only rifle officially called the AR-10.
ArmaLite AR-10 rifles use their own proprietary barrel nut standard which is incompatible with most AR-10/308 derivative rifle models on the market. The thread specifications for the AR-10 barrel nut are 1-7/16” and 18 TPI-3A. Besides ArmaLite, some popular rifle models that have licensed and use this barrel nut design include the Eagle Arms AR-10 the Noveske N6. Handguards compatible with these rifles are offered by LaRue, PRI, Badger Ordinance and Daniel Defense among others.

DPMS LR-308 Style Handguards

Rifle maker DPMS would go on to develop their own AR-10 style rifle called the LR-308, with the same general design but with a number of parts incompatible across platforms including the barrel nut/handguard. The barrel nut standard based on the popular DPMS LR-308 has become the most widely adopted on the market. The thread specifications for the LR-308 barrel nut are 1-7/16” and 16 TPI-2A. Numerous manufacturers make rifles using the LR-308 barrel nut standard including the Remington R25 and the Bushmaster 308 ORC.

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Please note that while the barrel nut standard for the DPMS LR-308 rifles has remained the same, there are two different versions of DPMS upper receiver that differ in the height of the receiver rail. Upper receivers manufactured before August 2009 have a high profile receiver rail, while upper receivers manufactured after August 2009 have a low profile receiver rail. Handguards made for the low profile receiver will still fit the older receiver, but the top rail will not align evenly with the receiver top rail.

DPMS GII Handguards

To confuse matters further, in 2014 DPMS released the DPMS GII 308 rifle. The DPMS GII is likewise, a DPMS made LR-308 rifle with an AR style design. However, the GII uses its own proprietary barrel nut standard.
GII barrel nuts are not interchangeable with LR-308 barrel nuts.

Other Non-Standard/Proprietary Handguards

Besides these standards, several other manufacturers of AR-10 style rifles use their own non-standard or proprietary style of barrel nut including Ruger SR-762 and the Daniel Defense DD5 V1.

AR-10/AR-308/LR-308 Free Float Rail/Handguard Compatibility List

To confirm what type of handguard will fit on your AR-10/308 rifle please refer to our handguard compatibility list below. The list is not comprehensive. If you have any additions, questions or updates, please contact us. Before purchasing a handguard, we highly recommending confirming compatibility with your rifle manufacturer.

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LR-308 Quad rails and Keymod Handguards, all backed with a Lifetime Warranty and our helpful customer service. Thank you for reading this article, if you have further questions regarding LR-308 Handguards please contact us for more help.